These days, foods are most generally packed and transported in finished portion or consumer packages of a single-use nature, i.e. packages which are intended to be used only once and thereafter destroyed or taken care of for other uses. Examples of such so-called single-use disposable packages are standard milk or juice packages of plastic coated paper which, after their contemplated use, are either incinerated or taken care of for material recycling or energy recovery at a plant for waste management. Other well-known examples of such portion or consumer packages are normal bottles of plastic or glass of the multi-use returnable type, for example packages which are intended to be used numerous times for the same purpose before being finally destroyed.
Irrespective of whether the package is of one or the other type, i.e. the single-use or multi-use package, the demands placed on it are that it must be easy to produce and handle and that it must be designed and constructed so as to afford the best possible protection to the product which is to be packed and transported in it. The good product protection implies, among other things, that the package must be of sufficient mechanical strength and configurational stability to withstand the outer forces to which the package may be subjected under normal handling, without being deformed or rupturing, and that the package must, moreover, be of sufficient physical and chemical tightness to prevent migration of liquid and/or gases through the package walls. In many cases, it is also required that the package be designed so as to permit aseptic packing of a product which is sterilized and packed under sterile conditions in a likewise sterilized package which, after filling, is sealed in such a manner that the packed product is not reinfected by harmful micro-organisms during its storage prior to consumption.
Generally, good product protection is achieved by a suitable selection of packaging material which, in itself, must be mechanically strong and configurationally stable and rigid and possess physical and chemical tightness properties so as to make possible the production of a configurationally stable package with the desired tightness properties for the product in question. Therefore, the material in the above-mentioned prior art single-use packages most usually consists of numerous layers of material which together impart to the package the desired properties. Thus, a known packaging material comprises a base or core layer of paper or cardboard which imparts to the package mechanical strength and configurational stability, as well as outer layers of polyethylene which make the package liquid-tight. In order to complement the package with tightness properties in respect of gases and other substances, the packaging material is provided with at least one further layer of a material of the desired tightness properties, for example aluminium or a barrier polymer.
For reasons which will be immediately apparent, the packaging material of the described laminated type is complex in its construction and composition which, consequently, becomes more complex the greater and more sophisticated the demands placed on the finished package in order to achieve optimum protection for the product which is to be packed.
Granted, the packaging material in packages of a multi-use nature, eg. glass or plastic bottles is simpler than the above-described packaging material of the laminate type, i.e. they generally consist of only one or possibly two material layers but, on the other hand, it is simultaneously required that the selected material satisfy all mechanical, physical and chemical demands which are placed on the package in order to provide optimum protection to the packed product. In itself, glass possesses good tightness properties against gases and is, moreover, a material possessing superior aroma barrier properties at the same time as it is configurationally stable--but the problem with packages of glass is that they are extremely sensitive to impact and jolts and, therefore, require extra care in order not to be damaged while being handled. Moreover, packages of glass are, as a rule, heavy--which makes their handling even more difficult.
Another material which is often employed in packages of the multi-use type is plastic which is lighter and less sensitive to impact and jolts than glass and, as a result, makes possible the production of more easily handleable packages. The problem inherent in known multi-use packages of plastic is, however, that they require plastics of special types and qualities in order to impart to the finished package the desired barrier properties and, moreover, the selected plastics must be of such a nature as to be well-suited for contact with foods.